1. Field of the Invention
This invention relates to a device for preventing idle rotation in a cylindrical ingot grinder, which device is used ideally in the operation of grinding a cylindrical part of a single crystal ingot for the purpose of preventing the ingot from being misshapen in consequence of the possible phenomenon of idle rotation.
2. Prior Art Statement
The semiconductor substrates to be used in semiconductor integrated circuits are manufactured by centering a single crystal ingot produced in the general shape of a round bar by such a single crystal growing method as the Czochralski method, grinding the cylindrical part of the ingot with a cylindrical grinder to finish it in a prescribed diameter, cutting the single crystal ingot perpendicularly to the axial direction thereof to obtain disklike substrates, and subjecting the substrates to the works of lapping, etching, polishing, etc.
A single crystal ingot 1 which terminates in generally conical parts 2 and 3 at the opposite ends thereof as illustrated in FIG. 8 is centered by machining to form between the generally conical parts 2 and 3 a cylindrical part 4 destined to be ground. Thus, the generally conical parts 2 and 3 and the cylindrical part 4 of the single crystal ingot 1 are both in a state deformed with a rough surface when the ingot 1 is subjected to the centering work. When the cylindrical part 4 is to be ground and finished by the use of a cylindrical grinder, either of the generally conical parts 2 and 3 is supported on a fast head stock side and the remainder on a foot stock side and the single crystal ingot 1 is rotated with a drive motor on the spindle side.
Since the conical parts 2 and 3 have a rough surface as mentioned above, however, an attempt to hold the single crystal ingot 1 as centered calls for a special device. The method of holding a given ingot by the opposite terminals thereof as illustrated in FIG. 9 has found popular acceptance to date. To be specific, this method comprises preparing a spindle side chuck and a tailstock side chuck containing a tapered hole having a smaller angle of inclination than the angle of inclination of the conical parts 2 and 3, mounting these chucks fast respectively on the fast head stock side and the foot stock side, and setting the single crystal ingot 1 fast in place for the sake of the work of grinding with the generally conical parts 2 and 3 thereof kept in tangential contact with the tapered holes.
During the work of grinding, the single crystal ingot 1 is rotated from the fast head stock side with the generally conical parts 2 and 3 thereof kept in tangential contact with the tapered holes of the spindle side chuck and the tailstock side chuck as described above. Since the supporting force produced jointly by the spindle side chuck and the tailstock side chuck is not sufficient for the purpose of keeping the single crystal ingot 1 conveniently for the work of grinding, the rotation from the fast head stock side is not transmitted infallibly to the single crystal ingot 1. There are times when the single crystal ingot 1 fails to rotate at all.
Even when the single crystal ingot 1 is rotated at all, slippage occurs between the spindle side chuck and the single crystal ingot 1 and, as a consequence, the revolution number of the spindle is not wholly transmitted to the single crystal ingot 1. The method under discussion, therefore, is at a disadvantage in suffering the single crystal ingot 1 to rotate at a far smaller revolution number than that of the rotation from the spindle side.
Further, since slippage is liable to occur between the tailstock side chuck and the single crystal ingot 1, the state of contact between the tapered hole of the tailstock side chuck and the generally conical part 3 of the single crystal ingot 1 varies. Because of this unsteady state of contact coupled with the rough surface of the generally conical part 3, the method entails the problem that the single crystal ingot 1 will vibrate during the work of grinding.
The decrease in the revolution number and the vibration prevent the work of cylindrical grinding from being fulfilled with high accuracy. The problem, therefore, arises that the attempt to manufacture semiconductor substrates with high quality ends up in failure. For the sake of attaining the work of grinding the single crystal ingot 1 advantageously, there has been heretofore followed the practice of keeping the state of rotation of the single crystal ingot under visual observation and keeping watch against the possible occurrence of vibration in the single crystal ingot and adjusting the pressing force exerted on the single crystal ingot along the axial direction thereof in due respect of the outcome of the visual observation so as to repress 3 the possible slippage between the two chucks and the generally conical parts 2 and 3 to the fullest possible extent.